To identify the molecular pathways involved in organ development, we are examining the endogenous role of genes initially identified based on their implication in human disease. Recently, it has been shown that patients with Noonan syndrome frequently have mis-sense mutations in the nonreceptor phosphatase Shp-2, a gene required downstream of FGF in the MARK signaling cascade. Clinical studies of Noonan patients, as well as analysis of mice mutant for Shp-2 demonstrate a fundamental role for the gene in both limb and heart development. A second example is Holt-Oram syndrome (HOS), a disease often associated with mutations in the coding region of the transcription factor TBX5, a gene also required for limb and heart development, leading to the suggestion the two genes may function in the same pathway. Consistent with this hypothesis, we have shown a direct link between the FGF/MAPK signal transduction pathway and TBX5 induction and transcriptional activity. The overall aim of this proposal is to integrate a transgenic and genetic approach in Xenopus with ongoing cellular and biochemical approaches to determine the precise endogenous role for SHP-2 and TBX5 in early organ development in the diploid frog Xenopus tropicalis (X. tropicalis). The long-term goal of these studies is to couple mutations and transgenic lines with biochemical and expression screens in Xenopus to identify the cellular and molecular pathways by which these factors function in early organ development. The specific aims of this proposal are: One, to establish Tbx5, Tbx20 and Eomesodermin cardiac specific reporter lines in X. tropicalis. Two, determine the role of Shp-2 and Tbx5 in organ development through the generation of an allelic series of Shp-2 and Tbx5 in X. tropicalis. [unreadable] [unreadable]